The invention relates to a driven axle, in particular a front axle, of a dual-track vehicle, in which a wheel-guiding control rod on the body of the vehicle or on a cross member connected to the body of the vehicle is stabilized spatially in a slightly elastic fashion via a control rod bearing on the body, and in which the control rod of the right-hand wheel is additionally connected to the control rod of the left-hand wheel via a coupling rod.
For prior art, reference is made, for example, to DE 23 55 588 C2, in which a front-wheel suspension for motor vehicles is disclosed having one upper triangular guidance control rod and one lower triangular guidance control rod, in which the lower rear guide arms of the left-hand and right-hand front wheel of the vehicle are supported elastically on a common, so-called, transverse yoke, which in turn is elastically connected to the lateral longitudinal bearings of the vehicle body. With this new construction, it is possible to largely prevent “front-end shaking,” i.e., the tendency of a vehicle to exhibit jolt-like vibrations caused by uneven driving surfaces and often reinforced by the natural vibrations of the vehicle drive system. The prior art discloses such an axle construction where, in other words, a wheel-guiding control rod of the left front wheel is connected to the corresponding guidance control rod of the right front wheel via a transverse yoke, for which the term “coupling rod” is used in the present case, for non-driven front wheels.
In the course of the development of motor vehicles to be more comfortable, in order to prevent front-end shaking or the like, the elasticity in the supports (or bearings) of the wheel-guiding control rods on the vehicle body or on a cross member and, in the case of a cross member, also the elasticity in the mounts of the cross member on the vehicle body, was adapted accordingly. In order to prevent the intensification of such vehicle vibrations due to the natural vibrations of the vehicle drive system, its bearings, known as motor bearings, were further improved accordingly.
However, it has been shown that, particularly when using internal combustion reciprocating piston engines with a low number of cylinders as vehicle drive systems, dynamic longitudinal vibrations on the vehicle wheels can result on the driven vehicle axle that, up to now, could only be mitigated by the use of additional absorbing masses and laborious adaptation of the relevant elastic suspensions or essentially prevented using extremely elaborate motor bearings.
The object of the present invention is to provide an improvement in this regard. This and other objects are achieved for a driven axle of a dual-track vehicle in which a wheel-guiding control rod on the body of the vehicle or on a cross member connected to the body of the vehicle is stabilized spatially in a slightly elastic fashion via a control rod bearing on the body, and in which the control rod of the right-hand wheel is additionally connected to the control rod of the left-hand wheel via a coupling rod. The coupling rod is exclusively supported on the above-mentioned left-hand and right-hand control rods, preferably near the respective control rod bearing that is on the body and disposed at an offset in the longitudinal direction of the vehicle relative to the associated wheel bearing or the midpoint of the wheel partially driven by the control rod. Further, in the coupling rod and/or in the connection between the coupling rod and one of the control rods supported opposite one another via the coupling rod, a mechanical low-pass filter is provided that is preferably embodied as an elastomer element.
It is known that cyclic irregularities of the vehicle drive system and, in particular, periodic fluctuations resulting therefrom of the torque exerted by the drive system via the wheel drive shafts cause corresponding fluctuations in the driving power transferred from the vehicle wheels to the driving surface. As a result, cyclic forces, known as disturbance forces, having a frequency determined by the roughly periodic fluctuations, are introduced into the vehicle body, which also disrupt the acoustics in the interior of the vehicle. It has now been shown that such opposing disturbance forces of an essentially equal degree introduced from the suspension of the left-hand and right-hand driven vehicle wheel into the vehicle body are able to compensate for one another, i.e., are able to at least approximately cancel each other out, if a pair of corresponding control rods on the left and right wheel suspensions are connected to one another via an essentially rigid component in the relevant frequency range in or with which these disturbance forces occur. Such an essentially rigid component is referred to in the present case as a coupling rod without the intent of creating any limitation to a purely “rod-shaped” component.
Preferably, this coupling rod is connected to the respective control rod near the control rod bearing on the body which, viewed in the longitudinal direction of the vehicle, is disposed at an offset relative to the associated wheel bearing or relative to the midpoint of the wheel partially driven by the control rod. In this manner, longitudinal vibrations of the driven wheel or wheel bearing resulting from cyclic irregularities of the drive system are converted to transverse vibrations of the region of the control rod near the bearing that now act via the control rod according to the invention originating from the left-hand control rod and the right-hand control rod opposite one another, thus canceling one another out.
The transmission or redirection of the cyclic irregularities of the drive system from longitudinal vibrations of the wheel or wheel bearing to transverse vibrations of a section or region of the control rod described up to now is particularly effective in the case of triangular transverse control rods, which are known to the skilled practitioner, but normally have a single connection point to the wheel bearing and to mounting points on the vehicle body or on a cross member connected therebetween.
A coupling rod according to the invention, of which a plurality may also be provided on one axle, differs significantly from the so-called transverse yoke in the prior art described at the outset. Namely, the latter is connected on both ends directly to the vehicle body via an elastic bearing, i.e., mounted directly on the vehicle body, and the respective left-hand or right-hand (guide) control rod is also supported via an elastic bearing on the transverse yoke; each control rod is able to introduce forces in the longitudinal direction of the vehicle and in the transverse direction of the vehicle as well as in the direction of the vertical axis of the vehicle into the transverse yoke, which then in turn conducts these forces into the vehicle body in all three dimensions. In other words, in the prior art, each of the control rods supported on the transverse yoke is spatially supported on the transverse yoke, namely providing the degree of rotational play in all three dimensions necessary for the compression and rebound movement of the wheel guided by the control rod, among other things, and the transverse yoke is in turn supported spatially, namely in all three dimensions, on the vehicle body.
In contrast, in the present invention, each of the two control rods connected to one another via the at least one coupling rod according to the invention is supported initially in a slightly elastic fashion directly on the vehicle body, in a spatial fashion in each control rod bearing, i.e., in the longitudinal and transverse directions of the vehicle and in the direction of the vertical axis of the vehicle with the necessary degree of rotational play for the compression and rebound movement, i.e., the wheel lift of the wheel guided by the control rod, among other things. Preferably, at least one coupling rod according to the invention is attached to the control rod in the vicinity of the control rod bearing, which is slightly elastic as is customary, the coupling rod itself not being supported at any other point. This coupling rod connects the control rod of the left vehicle wheel to the corresponding control rod of the right vehicle wheel and thus runs at least approximately in the transverse direction of the vehicle. The transfer of force through the coupling rod from the left-hand control rod to the right-hand control rod and vice versa can therefore occur naturally only in the transverse direction of the vehicle, more precisely in the direction of the coupling rod, in particular if a ball-and-socket joint is provided for the connection between the coupling rod and each control rod. The ball-and-socket joint should preferably be at least approximately free of play so as to allow an essentially rigid support of the two above-mentioned control rods relative to one another via the coupling rod according to the invention. In other words, the connection according to the invention between the coupling rod and the respective control rod is structured in such a way that it is virtually only able to transfer forces oriented in the longitudinal direction of the coupling rod from each control rod into the coupling rod, with the spatial, namely three-dimensional support of each control rod on the vehicle body explicitly not occurring by way of the coupling rod, in contrast to the prior art mentioned at the outset.
Regarding the above-mentioned term “relevant frequency range” of the essentially rigid component, for example, in the form of the so-called coupling rod, it is particularly advantageous for this rigidity to be in effect essentially only with regard to relatively high-frequency disturbance forces, i.e., with regard to the cyclic irregularities of the drive system discussed above or the resulting fluctuations in the driving forces exerted by the driven vehicle wheels on the driving surface, which naturally have a higher frequency than fluctuations in the transverse forces conducted between the wheels and the driving surface, i.e., cornering forces. With regard to fluctuations in the cornering forces introduced into the wheel suspension or axle via the wheels, a coupling rod according to the invention should be not at all or at least only slightly effective, i.e., significantly less effective, in order to maintain the otherwise desired individual wheel suspension and to prevent a direct influence of the wheel suspension of the left wheel on that of the right wheel (and vice versa). The latter is shown according to the invention in that a “mechanical” low-pass filter is provided in the coupling rod and/or in the connection between the coupling rod and one of the control rods supported opposite one another via the coupling rod. Such a mechanical low-pass filter essentially cancels the rigidity of the coupling rod (or the like) in low-frequency ranges in or with which the cornering forces act on the wheels, such that virtually no forces are transmitted via the coupling rod in these low-frequency ranges. The low-pass filter according to the invention allows low-frequency forces to simply pass without said forces being transmitted by the coupling rod according to the invention. In contrast, the low-pass filter according to the invention blocks higher-frequency ranges in or with which the above-mentioned disturbance forces resulting from the cyclic irregularity of the vehicle drive system occur, as a result of which the coupling rod according to the invention then transmits the disturbance forces as desired between the left-hand and right-hand control rods.
Preferably, the above-mentioned low-pass filter may be an elastomer element embodied in a suitable fashion with regard to the required property described in detail above. Alternatively, however, it may also be a suitably structured spring damper. Thus, in order to prevent or at least reduce mutual influence on elasto-kinematics by the right and left wheel of an axle equipped with at least one coupling rod as described above, the insertion of an additional component acting as a mechanical low-pass filter into the tension/compression load path of the coupling rod is recommended. In addition to a bushing having an elastomer element with the frequency-dependent hysteresis based on its material properties, a suitable spring damper may also be provided for this purpose.
On an axle as described up to this point, the forced vibrations of relatively high frequency conducted from the vehicle drive system into the axle which, in the prior art common up to now (individual wheel suspension without coupling rod and without a “transverse yoke”), are conducted into the vehicle body, i.e., into the carriage, are mutually compensated using a connection according to the invention via the coupling rod within the connection of a left-hand and right-hand wheel-guiding control rod. For example, in a three-cylinder internal combustion engine as the vehicle drive system, this frequency corresponds to 1.5 times the engine order. Despite this connection, the wheel-guiding control rod according to the general prior art (individual wheel suspension without a coupling rod and without a “transverse yoke”) can be connected via elastic bearings directly, or indirectly via a cross member, to the vehicle body for the regular decoupling of other vibration portions. A deep-pass filter directly integrated into the coupling rod has a greater rigidity at higher frequencies and transmits the disruptive, higher-frequency, vibrations that originate from the internal combustion engine in a significantly more pronounced manner than forces with low frequencies, thus achieving their direct compensation. The relatively slow variations in force, in particular from cornering forces that are introduced by the chassis and advantageously act on the elasto-kinematics of the respective side of the vehicle, are kept away from the other side of the vehicle because an elastomer element acting as a deep-pass filter or a spring damper mentioned above allows relatively slow relative movements of both parts of a coupling rod into which such a mechanical deep-pass filter is integrated or between which coupling rod parts such a mechanical deep-pass filter has been installed.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.